Parasitoid: what is it?

Parasitoids are insects which develop at the expense of others arthropods : at the immature stage of larva or of nymph, they consume the tissues of another host animal, which leads to its death. As adults, the insects parasitoids are free. The female will look for a new host to lay her eggs.

Parasitoid insects belong to different orders: Hymenoptera, diptera, beetles… Some parasitoids attack a variety of hosts, while others are more specialized. Parasitoids develop either inside the host (endoparasitoids) or outside (ectoparasitoids). Parasitoid insects are particularly interesting in the context of biological control to eliminate species harmful to crops. Often the pests are species exotic ; it is then necessary to bring back an effective natural parasitoid to recreate the host-parasitoid balance in their original environment. However, biological control also raises ecological questions, because there can be unforeseen side effects: for example if the parasitoid attacks another species, transmits diseases…

Examples of parasitoid insects

There are more than 80,000 species of parasitoids described in the world, including a majority of Hymenoptera, such as the parasitoid wasps. In biological control, the following parasitoid insects are used, for example:

• the first parasitoid insect used in biological control would be a predatory ladybug, Rodolia cardinalis. It has made it possible to fight against the cochineal native to Australia, Icerya purchasi, which plagued citrus crops in California;
• the trichogramma, Trichogramma brassicae, is a small wasp that lays its eggs in those of the moth. These insects therefore provide a solution against this caterpillar which ravages the fields of But, by limiting the use of phytosanitary products;
• Trichogramma counts different species that are used in fields of cereals, cotton, cane sugar, vegetable crops… In general, Trichogramma lay eggs in Lepidoptera eggs;
• the microwasp Encarsia formosa helps to fight against the white fly which damages the vegetable garden.